System for monitoring ablation size

ABSTRACT

A system for monitoring ablation size is provided. The system includes a power source including a microprocessor for executing one or more control algorithms. A microwave antenna is configured to deliver microwave energy from the power source to tissue to form an ablation zone. A plurality of spaced-apart electrodes is operably disposed along a length of the microwave antenna. The plurality of spaced-apart electrodes is disposed in electrical communication with one another and each of the plurality of spaced-apart electrodes has a threshold impedance associated therewith corresponding to the radius of the ablation zone.

BACKGROUND

1. Technical Field

The present disclosure relates to systems and methods that may be usedin tissue ablation procedures. More particularly, the present disclosurerelates to systems and methods for monitoring ablation size duringtissue ablation procedures in real-time.

2. Background of Related Art

In the treatment of diseases such as cancer, certain types of cancercells have been found to denature at elevated temperatures (which areslightly lower than temperatures normally injurious to healthy cells).These types of treatments, known generally as hyperthermia therapy,typically utilize electromagnetic radiation to heat diseased cells totemperatures above 41° C. while maintaining adjacent healthy cells atlower temperatures where irreversible cell destruction will not occur.Procedures utilizing electromagnetic radiation to heat tissue mayinclude ablation of the tissue.

Microwave ablation procedures, e.g., such as those performed formenorrhagia, are typically done to ablate the targeted tissue todenature or kill the tissue. Many procedures and types of devicesutilizing electromagnetic radiation therapy are known in the art. Suchmicrowave therapy is typically used in the treatment of tissue andorgans such as the prostate, heart, and liver.

One non-invasive procedure generally involves the treatment of tissue(e.g., a tumor) underlying the skin via the use of microwave energy. Themicrowave energy is able to non-invasively penetrate the skin to reachthe underlying tissue. However, this non-invasive procedure may resultin the unwanted heating of healthy tissue. Thus, the non-invasive use ofmicrowave energy requires a great deal of control.

Currently, there are several types of systems and methods for monitoringablation zone size. In certain instances, one or more types of sensors(or other suitable devices) are operably associated with the microwaveablation device. For example, in a microwave ablation device thatincludes a monopole antenna configuration, an elongated microwaveconductor may be in operative communication with a sensor exposed at anend of the microwave conductor. This type of sensor is sometimessurrounded by a dielectric sleeve.

Typically, the foregoing types of sensors are configured to function(e.g., provide feedback to a controller for controlling the power outputof a power source) when the microwave ablation device is inactive, i.e.,not radiating. That is, the foregoing sensors do not function inreal-time. Typically, the power source is powered off or pulsed off whenthe sensors are providing feedback (e.g., tissue temperature) to thecontroller and/or other device(s) configured to control the powersource.

SUMMARY

The present disclosure provides a system for monitoring ablation size inreal-time. The system includes a power source. A microwave antenna isconfigured to deliver microwave energy from the power source to tissueto form an ablation zone. A plurality of spaced-apart electrodes isoperably disposed along a length of the microwave antenna. Theelectrodes are disposed in electrical communication with one another.Each of the electrodes has a threshold impedance associated therewithcorresponding to the radius of the ablation zone.

The present disclosure provides a microwave antenna adapted to connectto a power source configured for performing an ablation procedure. Themicrowave antenna includes a radiating section configured to delivermicrowave energy from the power source to tissue to form an ablationzone. The microwave antenna includes a plurality of spaced-apartelectrodes operably disposed along a length of the microwave antenna.The electrodes are disposed in electrical communication with oneanother. Each of the electrodes has a threshold impedance associatedtherewith corresponding to the radius of the ablation zone.

The present disclosure also provides a method for monitoring tissueundergoing ablation. The method includes the initial step oftransmitting microwave energy from a power source to a microwave antennato form a tissue ablation zone. A step of the method includes monitoringone or more electrodes impedance along the microwave antenna as thetissue ablation zone forms. Triggering a detection signal when apredetermined electrode impedance is reached at the at least oneelectrode along the microwave antenna is another step of the method. Themethod includes adjusting the amount of microwave energy from the powersource to the microwave antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a perspective view of a system for monitoring ablation sizeaccording to an embodiment of the present disclosure;

FIG. 2 is partial, side view illustrating internal components of adistal tip of a microwave antenna depicted in FIG. 1;

FIG. 3 is a functional block diagram showing a power source for use withthe system depicted in FIG. 1;

FIG. 4A is a schematic, plan view of a tip of the microwave antennadepicted in FIG. 2 illustrating radial ablation zones having a generallyspherical configuration;

FIG. 4B is a schematic, plan view of a tip of the microwave antennadepicted in FIG. 2 illustrating radial ablation zones having a generallyellipsoidal configuration;

FIG. 5A is a schematic, plan view of a portion of the microwave antennadepicted in FIG. 1 showing a sequenced insertion of the microwaveantenna into tissue;

FIG. 5B is a graphical representation of corresponding impedancesassociated with respective electrodes of the microwave antenna depictedin FIG. 5A;

FIG. 6 is a flow chart illustrating a method for monitoring temperatureof tissue undergoing ablation in accordance with the present disclosure;

FIG. 7 is partial, side view illustrating internal components of adistal tip of a microwave antenna according to an alternate embodimentof the present disclosure; and

FIG. 8 is a functional block diagram showing a power source for use withthe microwave antenna depicted in FIG. 7.

DETAILED DESCRIPTION

Embodiments of the presently disclosed system and method are describedin detail with reference to the drawing figures wherein like referencenumerals identify similar or identical elements. As used herein and asis traditional, the term “distal” refers to the portion which isfurthest from the user and the term “proximal” refers to the portionthat is closest to the user. In addition, terms such as “above”,“below”, “forward”, “rearward”, etc. refer to the orientation of thefigures or the direction of components and are simply used forconvenience of description.

Referring now to FIGS. 1 and 2, and initially with reference to FIG. 1,a system for monitoring ablation size in accordance with an embodimentof the present disclosure is designated 10. A microwave antenna 12operably couples to generator 100 and includes a controller 200 thatconnects to the generator 100 via a flexible coaxial cable 14. In thisinstance, generator 100 is configured to provide microwave energy at anoperational frequency from about 500 MHz to about 10 GHz. Microwaveantenna 12 includes a radiating section or portion 16 (FIGS. 1 and 2)that is connected by a feedline or shaft 18 to coaxial cable 14 andextends from the proximal end of the microwave antenna 12. Cable 14includes an inner conductor 13 that is operably disposed within theshaft 18 and in electrical communication with a radiating section 16(FIGS. 1 and 2). Microwave antenna 12 couples to the cable 14 through aconnection hub 22. The connection hub 22 includes an outlet fluid port24 and an inlet fluid port 26 connected in fluid communication with asheath or cannula 28 (FIG. 2). Cannula 28 is configured to circulatecoolant fluid 30 from ports 24 and 26 around the antenna assembly 12 viarespective fluid lumens 32 and 34 (FIG. 2). Ports 24 and 26, in turn,couple to a supply pump 40. For a more detailed description of themicrowave antenna 12 and operative components associated therewith,reference is made to commonly-owned U.S. patent application Ser. No.12/401,268 filed on Mar. 10, 2009.

With continued reference to FIGS. 1 and 2, two or more spaced-apartelectrodes 52 and 54 are operably disposed along a length of the shaft18. More particularly, the electrodes 52 and 54 are disposed inproximity to a distal end 19 of the shaft 18. In the embodimentillustrated in FIG. 2, electrodes 52 include a series of proximalspaced-apart electrodes 52 a-52 h and a distal electrode 54. As definedherein, a series of electrodes is meant to mean two or more electrodes.For purposes herein, the series of proximal spaced-apart electrodes 52a-52 h referred to proximal electrodes 52. The configuration of theelectrodes 52 and 54 enables physical space sampling of an ablationsite. More particularly, in one particular embodiment, during thedelivery of microwave energy to the microwave antenna 12, impedancebetween one or more of the proximal electrodes 52, e.g., proximalelectrode 52 a, and the distal electrode 54 is measured and comparedwith known impedance values associated with the microwave antenna 12and/or proximal electrodes 52, e.g., proximal electrode 52 a. Theconfiguration of each proximal electrodes 52 a-52 h and distal electrode54 provides a separate closed loop path for current to flow, i.e., anelectrical circuit, when the microwave antenna 12 is inserted intotissue at a target tissue site. Impedance is measured between eachproximal electrode 52 a-52 h and the distal electrode 54, as describedin greater detail below.

Proximal electrodes 52 a-52 h may be formed from any suitable conductiveor partially conductive material. For example, proximal electrodes 52-52h may be formed from copper, silver, gold, etc. Proximal electrodes 52a-52 h are operably positioned along an outer peripheral surface 38 ofthe shaft 18 in a manner suitable for the intended purposes describedherein. In embodiments, the proximal electrodes 52 a-52 h may extendcircumferentially along the outer peripheral surface 38 or partiallyalong a length of the shaft 18. In the illustrative embodiment, proximalelectrodes 52 a-52 h extend partially along the outer peripheral surface38 in a linear manner forming a generally linear array along the outerperipheral surface 38 of the shaft 18. Proximal electrodes 52 a-52 h maybe secured to the outer peripheral surface 38 and/or the shaft 18 viaany suitable method(s). In one particular embodiment, the proximalelectrodes 52 a-52 h are secured to the outer peripheral surface 38 viaan epoxy adhesive (or other suitable adhesive). Proximal electrodes 52a-52 h are in operative communication with one or more modules, e.g.,ablation zone control module 232 (AZCM), associated with the generator100 and/or controller 200. To this end, a portion of the proximalelectrodes 52 a-52 h connects to one or more electrical leads (notexplicitly shown) that provide an electrical interface for the proximalelectrodes 52 a-52 h and the AZCM 232. Moreover, the electrical leadsprovide an electrical interface that supplies current, i.e., from acurrent source (or other suitable device configured to generate current,voltage source, power source, etc.) to the proximal electrodes 52 a-52h.

In certain embodiments, one or more sensors, e.g., sensors 53 a-53 h,may be in operative communication with a respective one or correspondingproximal electrode 52 a-52 h (as best seen in FIG. 2). In this instance,the sensors 53 a-53 h may be configured to provide real-time informationpertaining to the proximal electrodes 52 a-52 h. More particularly, thesensors 53 a-53 h may be configured to provide real-time informationpertaining to one or more electrical parameters (e.g., impedance, power,voltage, current, etc.) and/or other parameters associated with theproximal electrodes 52 a-52 h. More particularly, the sensors 53 a-53 hmay be in the form of one or more types of thermal sensors such as, forexample, a thermocouple, a thermistor, an optical fiber, etc. In oneparticular embodiment, the sensors 53 a-53 h are thermocouples 53 a-53h.

Distal electrode 54 may be formed from any suitable conductive orpartially conductive material, e.g., copper, silver, gold, etc. Distalelectrode 54 may have any suitable configuration. For illustrativepurposes, distal electrode 54 is shown operably disposed at a distal tip21 of the shaft 18. In the illustrated embodiment, distal electrode 54defines a conductive tissue piercing tip. In this instance, the distalelectrode 54 facilitates insertion of the microwave antenna 12 intotissue at a target tissue site. Alternatively, distal electrode 54 mayhave a relatively blunt configuration. An electrical lead (notexplicitly shown) provides an electrical interface for returning currentfrom the distal electrode 54 back to the current source. In certainembodiments, distal electrode 54 may be in operative communication withone or more modules, e.g., AZCM 232, associated with the generator 100and/or controller 200. In this instance, the electrical lead may providean electrical interface for the distal electrode 54 and the AZCM 232.

In certain embodiments, one or more sensors, e.g., sensor 55, may be inoperative communication with the distal electrodes 54 (see FIG. 2, forexample) and may provide information relevant to the proper operation ofdistal electrode 54 to the AZCM 232. Sensor 55 may be any suitable typeof sensor such as, for example, one or more types of thermal sensorspreviously described above, e.g., a thermocouple.

A dielectric sheath 60 having a suitable thickness and made from asuitable material is operably positioned along a length of the microwaveantenna 12 and substantially encases the proximal electrodes 52 a-52 hand distal electrode 54 in a manner that allows current to flow from theproximal electrodes 52 a-52 h to the distal electrode 54. Dielectricsheath 60 may be made from any suitable material and may be affixed tothe microwave antenna 12 by any suitable affixing methods. In theillustrated embodiment, the dielectric sheath 60 is a vapor depositeddielectric material, such as, for example, parylene, that is applied tothe microwave antenna 12. Substantially encasing the microwave antenna12 with dielectric sheath 60 results in capacitive impedance that canallow RF current flow to/from the electrodes 52 a-52 h and tissue. Moreparticularly, during transmission of microwave energy from the generator100 to the microwave antenna 12 and when the proximal electrodes 52 a-52h and distal electrode 54 are positioned within tissue adjacent a targettissue site, current flows from proximal electrodes 52 a-52 h to theelectrode 54. Dielectric sheath 60 is configured to focus currentdensities “I” at the proximal electrodes 52 a-52 h and/or the distalelectrode 54, which, in turn, provides comprehensive and/or moreaccurate measurements of impedance at the proximal electrode 52 a-52 h,as best seen in FIG. 2. In certain embodiments, the dielectric sheath 60may fully encase the proximal electrodes 52 a-52 h and distal electrode54. In this instance, the dielectric sheath 60 includes a thickness thatallows current to pass from the proximal electrodes 52 a-52 h throughthe dielectric sheath 60 and to the distal electrode 54. In oneparticular embodiment, the thickness of the dielectric material of thedielectric sheath 60 ranges from about 0.0001 inches to about 0.001inches.

As mentioned above, proximal electrodes 52 a-52 h (and in some instancesdistal electrode 54) is in operative communication with the generator100 including AZCM 232 and/or controller 200. More particularly, theproximal electrodes 52 a-52 h and distal electrode 54 couple to thegenerator 100 and/or controller 200 via one or more suitable conductivemediums (e.g., a wire or cable 56) that extends from proximal electrodes52 a-52 h and distal electrode 54 to the proximal end of the microwaveantenna 12 and connects to the generator 100 (see FIG. 2, for example).In the illustrated embodiment, wire 56 is operably disposed within cable14. Wire 56 electrically connects to the proximal electrodes 52 a-52 hand distal electrode 54 via the one or more leads previously described.The configuration of wire 56, proximal electrodes 52 a-52 h and distalelectrode 54 forms a closed loop current path when the electrodes 52 anddistal electrode 54 are positioned within tissue adjacent a targettissue site. In the illustrated embodiment, the wire 56 extends alongthe outer peripheral surface 38 of the shaft 18 and is encased by thedielectric sheath 60. Alternatively, the wire 56 may extend within andalong a length of the shaft 18.

With reference to FIG. 3, a schematic black diagram of the generator 100is illustrated. The generator 100 includes a controller 200 includingone or more modules (e.g., an AZCM 232), a power supply 137, a microwaveoutput stage 138. In this instance, generator 100 is described withrespect to the delivery of microwave energy. The power supply 137provides DC power to the microwave output stage 138 which then convertsthe DC power into microwave energy and delivers the microwave energy tothe radiating section 16 of the microwave antenna 12 (see FIG. 2). Inthe illustrated embodiment, a portion of the DC power is directed to theAZCM 232, described in greater detail below. The controller 200 mayinclude analog and/or logic circuitry for processing sensed analogresponses, e.g., impedance response, generated by the proximalelectrodes 52 a-52 h and determining the control signals that are sentto the generator 100 and/or supply pump 40 via the microprocessor 235.More particularly, the controller 200 accepts one or more signalsindicative of impedance associated with proximal electrodes 52 a-52 hadjacent an ablation zone and/or the microwave antenna 12, namely, thesignals generated by the AZCM 232 as a result of the impedance measuredand/or produced by proximal electrodes 52 a-52 h. One or more modulese.g., AZCM 232, of the controller 200 monitors and/or analyzes theimpedance produced by the proximal electrodes 52 a-52 h and determinesif a threshold impedance has been met. If the threshold impedance hasbeen met, then the AZCM 232, microprocessor 235 and/or the controller200 instructs the generator 100 to adjust the microwave output stage 138and/or the power supply 137 accordingly. Additionally, the controller200 may also signal the supply pump to adjust the amount of coolingfluid to the microwave antenna 12 and/or the surrounding tissue.

The controller 200 includes microprocessor 235 having memory 236 whichmay be volatile type memory (e.g., RAM) and/or non-volatile type memory(e.g., flash media, disk media, etc.). In the illustrated embodiment,the microprocessor 235 is in operative communication with the powersupply 137 and/or microwave output stage 138 allowing the microprocessor235 to control the output of the generator 100 according to either openand/or closed control loop schemes. The microprocessor 235 is capable ofexecuting software instructions for processing data received by the AZCM232, and for outputting control signals to the generator 100 and/orsupply pump 40, accordingly. The software instructions, which areexecutable by the controller 200, are stored in the memory 236.

In accordance with the present disclosure, the microwave antenna 12 isconfigured to create an ablation zone “A” having any suitableconfiguration, such as, for example, spherical (FIG. 4A), hemispherical,ellipsoidal (FIG. 4B where the ablation zone is designated “A-2”), andso forth. In one particular embodiment, microwave antenna 12 isconfigured to create an ablation zone “A” that is spherical (FIG. 4A).To facilitate understanding of the present disclosure, ablation zone “A”is being defined having a plurality of concentric ablation zones havingradii r₁-r₈ when measured from the center of the ablation zone “A,”collectively referred to as radii r.

With reference to FIGS. 5A and 5B, proximal electrodes 52 a-52 h incombination with distal electrode 54 are configured to providecomprehensive monitoring of an ablation zone “A” (FIGS. 4A and 5A atmicrowave position J). More particularly, the concept of the integrationof impedance Z associated with proximal electrodes 52 over time may beused to indicate tissue damage, e.g., death or necrosis. For a givenmicrowave antenna 12, each of the proximal electrodes 52 a-52 h has apredetermined threshold impedance Z associated therewith. Thepredetermined threshold impedance Z associated with a correspondingelectrode 52 a-52 h, e.g., electrode 52 a, and a corresponding radius“r,” e.g., r1, may be determined via any suitable methods. For example,predetermined threshold impedances Z may be determined via knownexperimental test data, model equations, functions and graphs, orcombination thereof.

In one particular embodiment, a control algorithm of the presentdisclosure uses known (or in certain instances predicted) thresholdimpedances Z at specific radii to create an ablation zone “A” having aradius “r.” That is, impedances Z associated with proximal electrodes 52a-52 h that correspond to specific radii are compiled into one or morelook-up tables “D” and are stored in memory, e.g., memory 236,accessible by the microprocessor 235 and/or the AZCM 232 (FIG. 3). TheAZCM 232 includes control circuitry that receives information from theproximal electrodes 52 a-52 h, and provides the information and thesource of the information (e.g., the particular proximal electrode 52providing the information) to the controller 200 and/or microprocessor235. More particularly, AZCM 232 monitors the impedance Z at theproximal electrodes 52, e.g., proximal electrode 52 a, and triggers acommand signal in response to the proximal electrode 52 a reaching apredetermined impedance Z such that the electrosurgical output powerfrom the generator 100 may be adjusted (see FIG. 5A at microwave antenna12 position F).

AZCM 232 may be configured to monitor impedance Z at the proximalelectrodes 52 a-52 h by any known method(s). For example, in oneparticular embodiment, the AZCM 232 utilizes one or more equations(V=I×Z) to calculate the impedance at a particular electrode 52 a-52 h.In this instance, the voltage V and current I is known and the AZCM 232calculates the impedance Z. Alternatively, or in combination therewith,the sensor(s) 53 a-53 h may provide thermal measurements at a respectiveelectrode 52 a-52 h. With the impedance of a respective proximalelectrode 52 a-52 h calculated and/or determined, AZCM 232,microprocessor 235 and/or controller 200 may access the one or morelook-up tables “D” and confirm that the threshold impedance Z has beenmet and, subsequently, instruct the generator 100 to adjust the amountof microwave energy being delivered to the microwave antenna 12, seeFIG. 5B at corresponding graphical representation F. This combination ofevents will provide an ablation zone “A” with a radius approximatelyequal to r3, i.e., an ablation zone approximately equal to 3 cm by 1 cm.It should be noted, that in this instance, the ablation zone “A” is moreellipsoidal than spherical. In embodiments, one or more controlalgorithms may utilize interpolation between the radii associated withthe electrodes 52 a-52 h to calculate impedance between discreetlymeasured radii, e.g., impedance measured between electrode 52 a andelectrode 52 b. More particularly, various (and commonly known)interpolation techniques may be utilized via curve fitting along theelectrodes 52 a-52 h.

In certain instances, the one or more data look-up tables may be storedinto memory during the manufacture process of the generator 100 and/orcontroller 200 or downloaded during programming; this is particularlyuseful in the instance where the generator 100 is configured for usewith a single type of microwave antenna. Alternatively, the one or moredata look-up tables may be downloaded into memory 236 at a time prior touse of the system 10; this is particularly useful in the instance wherethe generator 100 is configured for use with multiple microwave antennasthat are configured to perform various ablation procedures.

In one particular embodiment, data look-up table “D” may be stored in amemory storage device 73 associated with the microwave antenna 12. Moreparticularly, a data look-up table “D” may be stored in a memory storagedevice 73 operatively associated with the microwave antenna 12 and maybe downloaded, read and stored into microprocessor 235 and/or memory 236and, subsequently, accessed and utilized in a manner described above;this would dispose of the step of reprogramming the generator 100 and/orcontroller 200 for a specific microwave antenna. More particularly, thememory storage device 73 may be operably disposed on the microwaveantenna 12, such as, for example, on or adjacent the hub 22 (FIG. 1). Inthis instance, when a user connects the microwave antenna 12 to thegenerator 100, the information contained in the memory storage devicemay be automatically read, downloaded and stored into the generator 100and accessed for future use. The memory storage device 73 may alsoinclude information pertaining to the microwave antenna 12. Information,such as, for example, the type of microwave antenna, the type of tissuethat the microwave antenna is configured to treat, the type of ablationzone desired, etc., may be stored into the storage device 73 associatedwith the microwave antenna 12.

In the embodiment illustrated in FIG. 1, the generator 100 is shownoperably coupled to fluid supply pump 40. The supply pump 40 is, inturn, operably coupled to a supply tank 44. In embodiments, themicroprocessor 235 is in operative communication with the supply pump 40via one or more suitable types of interfaces, e.g., a port 140operatively disposed on the generator 100, that allows themicroprocessor 235 to control the output of a cooling fluid 30 from thesupply pump 40 to the microwave antenna 12 according to either openand/or closed control loop schemes. The controller 200 may signal thesupply pump 40 to control the output of cooling fluid 30 from the supplytank 44 to the microwave antenna 12. In this way, cooling fluid 30 isautomatically circulated to the microwave antenna 12 and back to thesupply pump 40. In certain embodiments, a clinician may manually controlthe supply pump 40 to cause cooling fluid 30 to be expelled from themicrowave antenna 12 into and/or proximate the surrounding tissue.

Operation of system 10 is now described. For illustrative purposes,proximal electrodes 52 a-52 h may be considered as individual anodes anddistal electrode 54 may be considered as a cathode. Each of the proximalelectrodes 52 a-52 h includes a predetermined threshold impedance Z thathas been previously determined by any of the aforementioned methods,e.g., experimental test data. Initially, microwave antenna 12 isconnected to generator 100. In one particular embodiment, one or moremodules, e.g., AZCM 232, associated with the generator 100 and/orcontroller 200 reads and/or downloads data, e.g., the type of microwaveantenna, the type of tissue that is to be treated, data look-up tables,etc., from storage device 73 associated with the antenna 12. In thepresent example, the AZCM module 232 recognizes the microwave antenna 12as having 8 proximal electrodes 52 a-52 h each with a predeterminedthreshold impedance Z that corresponds to a specific ablation zone “A.”In one particular embodiment, the generator 100 prompts a user to enterthe desired ablation zone size, e.g., ablation zone equal to 5 cm by 5cm having a generally spherical configuration, see FIGS. 4A and 5A atmicrowave antenna 12 position J. After a user inputs the desiredablation zone size information, the AZCM 232 matches the desiredablation zone size with the particular electrode 52 a-52 h, e.g.,proximal electrode 52 h. The AZCM 232 sets the threshold impedance Z,e.g., Z ablated, for that particular proximal electrode. Thereafter, thegenerator 100 may be activated supplying microwave energy to theradiating section 16 of the microwave antenna 12 such that the tissuemay be ablated.

AZCM 232 transmits DC current (or in some instances an RF signal, e.g.,in the KHz or low MHz frequency spectrum) to each of the proximalelectrodes 52 a-52 h. Prior to insertion of microwave antenna 12 intotissue “T”, impedance Z associated with each of the plurality ofproximal electrodes 52 a-52 h is relatively high, e.g., infinite; thisis because an open circuit exists between the proximal electrodes 52a-52 h and the distal electrode 54. Microwave antenna 12 includingproximal electrodes 52 a-52 h may then be positioned within tissue (seeFIGS. 5A and 5B at microwave antenna 12 position E and correspondinggraph at position E, respectively) adjacent a target tissue site.Impedance Z associated with each of the plurality of proximal electrodes52 a-52 h is relatively low, e.g., non-zero; this is because uncookedtissue has a finite or infinitesimal impedance. During tissue ablation,the AZCM 232 monitors impedance Z of the proximal electrodes 52 a-52 h.During tissue ablation, when a predetermined threshold impedance isreached (such as the impedance Z that corresponds to radius r8) at theparticular proximal electrode 52 a-52 h, e.g., electrode 52 h, and isdetected by the AZCM 232, the AZCM 232 instructs the generator 100 toadjust the microwave energy accordingly. In the foregoing sequence ofevents, the proximal electrodes 52 a-52 h, distal electrode 54 and AZCM232 function in real-time controlling the amount of microwave energy tothe ablation zone such that a uniform ablation zone of suitableproportion is formed with minimal or no damage to adjacent tissue.

It should be noted that at any time during the ablation procedure, auser may adjust the previously inputted ablation zone size information.More particularly, if a user determines that during the course of themicrowave ablation procedure the original ablation zone size needs to beadjusted, e.g., original ablation zone size is too big or too small, auser may simply input the new ablation zone size, and the AZCM 232 willadjust automatically. For example, if during the above example a userdecides to adjust the ablation zone size to 4 cm by 4 cm (see FIGS. 5Aand 5B at microwave antenna position D the AZCM 232 monitors proximalelectrode 52 e until proximal electrode 52 e reaches the predeterminedthreshold impedance Z.

With reference to FIG. 5 a method 400 for monitoring tissue undergoingablation is illustrated. At step 402, microwave energy from a generator100 is transmitted to a microwave antenna 12 adjacent a tissue ablationsite. At step, 404, one or more electrodes' impedance at the ablationsite is monitored. At step 406, a detection signal is triggered when apredetermined electrode impedance is reached at the one or moreelectrodes along the microwave antenna. At step 408, the amount ofmicrowave energy from the generator 200 to the microwave antenna may beadjusted.

From the foregoing and with reference to the various figure drawings,those skilled in the art will appreciate that certain modifications canalso be made to the present disclosure without departing from the scopeof the same. For example, the system 10 may be adapted to connect to anRF electrosurgical power source, e.g., an RF generator that includes oris in operative communication with one or more controllers 200 includingan AZCM 232.

While the electrodes 52 have been described herein as including a seriesof proximal electrodes 52 a-52 h and a distal electrode 54 that ispositioned at a distal tip 21 of the shaft 18, it is within the purviewof the present disclosure that the distal electrode 54 may be positionedanywhere along the shaft 18, e.g., positioned adjacent the series ofproximal electrodes 52 a-52 h. Or, in another embodiment, a distalelectrode 54 may not be utilized. In this instance, one of the series ofproximal electrodes 52 a-52 h may be configured to function in a manneras described above with respect to distal electrode 54.

In certain embodiments, it may prove useful not to utilize a lead wire56 that couples to distal electrode 54. In this instance, innerconductor 13 takes the place of the lead wire 56 and operably couples tothe distal electrode 54, see FIG. 7, for example. More particularly, oneor more types of DC blocks 58 are operatively associated with themicrowave antenna 12. More particularly, DC block 58 is operablydisposed within the generator 100 and in electrical communication withthe inner conductor 13, shown schematically in FIG. 8. The DC block 58prevents and/or limits direct current (DC) frequencies present at thedistal electrode 54 from interfering with the microwave signals producedby the radiating section 16. DC block 58 may be configured in a mannerthat is conventional in the art. More particularly, DC block 58 mayinclude one or more capacitors “C” configured in series with innerconductor 13 of the coaxial conductor 14, in series with an outerconductor (not explicitly shown) of the coaxial conductor 14, or inseries with both the inner conductor 13 and outer conductor of thecoaxial conductor 14. DC block 58 may be configured to function as anotch filter and designed to allow impedance measurement signals, i.e.,impedance measurement signals that are in the KHz frequency range. Inthe embodiment illustrated in FIG. 7, lead wire 56 couples to theplurality of electrodes 52 a-52 h in a manner described above. Lead wire56 is dimensioned to accommodate a respective RF signal that istransmitted to the distal electrode 54 and/or plurality of electrodes 52a-52 h from the AZCM 232.

AZCM 232 is configured to transmit an RF impedance measurement signal tothe proximal electrodes 52 a-52 h and/or the distal electrode 54. In theembodiment illustrated in FIG. 8, AZCM is configured to transmit an RFimpedance measurement signal to the proximal electrodes 52 a-52 h and/orthe distal electrode 54 that ranges from about 3 KHz to about 300 MHz.

Operation of system 10 that includes a generator 100 with a DC block 58that is in operative communication with a microwave antenna 12 issubstantially similar to that of a generator 100 without a DC block 58and, as a result thereof, is not described herein.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

What is claimed is:
 1. A system for monitoring ablation size,comprising: a power source having an electrical circuit that providesmicrowave energy; a microwave antenna including a radiating sectionconfigured to deliver the microwave energy from the power source totissue to form an ablation zone; and a plurality of spaced-apartelectrodes operably disposed along a length of the microwave antenna,the electrodes in electrical communication with one another, each of theelectrodes having a threshold impedance associated therewithcorresponding to the radius of the ablation zone, wherein the pluralityof spaced-apart electrodes includes a series of proximal spaced-apartelectrodes along the shaft and a distal electrode operably disposed at adistal tip of the shaft, and wherein a voltage potential is presentbetween at least one of the series of proximal spaced-apart electrodesand the distal electrode as a result of delivery of microwave energy tothe microwave antenna such that current flows between the at least oneproximal electrode and the distal electrode and returns to the powersource via a closed loop electrical circuit that is provided in themicrowave antenna and separate from the electrical circuit that providesmicrowave energy to the radiating section of the microwave antenna.
 2. Asystem according to claim 1, further including an ablation zone controlmodule in operative communication with the microwave antenna and thepower source and configured to instruct the power source to adjust theamount of microwave energy being delivered to the microwave antenna whena predetermined threshold impedance is generated by one of theelectrodes to create a uniform ablation zone of suitable proportion withminimal damage to adjacent tissue.
 3. A system according to claim 2,wherein the ablation zone control module and the plurality ofspaced-apart electrodes are activated when the power source isactivated.
 4. A system according to claim 2, wherein at least onecontrol algorithm operably associated with the ablation zone controlmodule utilizes at least one data look-up table that includesinformation pertaining to predetermined threshold impedance valuesassociated with the plurality of spaced-apart electrodes andcorresponding radii.
 5. A system according to claim 4, wherein theinformation pertaining to predetermined threshold impedance valuesassociated with the plurality of spaced-apart electrodes andcorresponding radii is pre-programmed into the power source andaccessible by one of the ablation zone control module and amicroprocessor.
 6. A system according to claim 4, wherein theinformation pertaining to predetermined threshold impedance valuesassociated with the plurality of spaced-apart electrodes andcorresponding radii is stored on the microwave antenna and downloadedinto a memory of the power source and accessible by one of the ablationzone control module and a microprocessor.
 7. A system according to claim1, wherein the plurality of spaced-apart electrodes is operablypositioned on a portion of a shaft associated with the microwaveantenna.
 8. A system according to claim 1, wherein a wire connects toeach of the series of proximal spaced-apart electrodes and the distalelectrode.
 9. A system according to claim 1, wherein a dielectricsheathing is operably positioned along a length of the microwave antennaand encases the series of proximally spaced-apart electrodes in a mannerthat allows current to flow between the series of proximallyspaced-apart electrodes and the distal electrode.
 10. A system accordingto claim 1, wherein the microwave antenna is configured to produce anablation zone that is one of spherical and ellipsoidal.
 11. A systemaccording to claim 1, further comprising: at least one fluid pumpconfigured to supply a cooling fluid to the microwave antenna forfacilitating cooling of one of the microwave antenna and tissue adjacentthe ablation zone.
 12. A microwave antenna adapted to connect to a powersource configured for performing an ablation procedure, comprising: aradiating section configured to deliver microwave energy from a powersource to tissue to form an ablation zone, the power source having anelectrical circuit that provides the microwave energy to the radiatingsection; and a plurality of spaced-apart electrodes operably disposedalong a length of the microwave antenna, the plurality of spaced-apartelectrodes disposed in electrical communication with one another, eachof the plurality of spaced-apart electrodes having a threshold impedanceassociated therewith corresponding to the radius of the ablation zone,wherein the plurality of spaced-apart electrodes includes a series ofproximal spaced-apart electrodes along the shaft and a distal electrodeoperably disposed at a distal tip of the shaft, and wherein a voltagepotential is present between at least one of the series of proximalspaced-apart electrodes and the distal electrode as a result of deliveryof microwave energy to the microwave antenna such that current flowsbetween the at least one proximal electrode and the distal electrode andreturns to the power source via a closed loop electrical circuit that isprovided in the microwave antenna and separate from the electricalcircuit that provides the microwave energy to the radiating section ofthe microwave antenna.
 13. A microwave antenna according to claim 12,wherein the plurality of spaced-apart electrodes are operably positionedon a portion of a shaft associated with the microwave antenna.
 14. Amicrowave antenna according to claim 12, wherein a wire connects each ofthe series of proximal spaced-apart electrodes and the distal electrode.15. A system according to claim 14, wherein a dielectric sheathing isoperably positioned along a length of the microwave antenna and encasesthe series of proximally spaced-apart electrodes in a manner that allowscurrent to flow between the series of proximally spaced-apart electrodesand the distal electrode.